1. Field of the Invention
This invention relates generally to fossil fuel refining by solvent extraction to produce a high yield refined product which is low in mineral matter and sulfur. More specifically, this invention produces a low ash refined product by contacting, for up to about three hours, ground fossil fuel with phenol solvent at a temperature of about 600.degree. to about 690.degree. F. and a corresponding saturation pressure of about 220 to about 430 psig. The phenol solvent separates the refined product from the fossil fuel by dissolution, leaving behind a carbonaceous high mineral content residue.
2. Description of the Prior Art
Solvent extraction of bituminous coals has been recognized as desirable for many years. M. W. Kiebler, in his article, "Extraction of a Bituminous Coal: Influence of the Nature of Solvents," published in Gas Journal, Vol. 232, Dec. 4, 1940, pages 433-436, teaches treatment of Pittsburgh Seam coal with a large number of organic solvents, including phenol, which was reported to dissolve from about 21 to about 40 percent of the coal, based on recovery of organic material, following residence times of 72-120 hours at temperatures of 302.degree. F. to 572.degree. F. and phenol being present, on a weight basis, in an amount of about 20 times the coal. Depolymerization of bituminous coals with phenol at 212.degree. F., wherein the reaction was catalyzed with boron trifluoride, which was found to be necessary to the depolymerization, was reported by L. A. Heredy and M. B. Neuworth, "Low Temperature Depolymerization of Bituminous Coal," Fuel, Vol. 41, pages 221-231, 1962. Solvent refining processes utilizing about 30 to 40 lbs. of hydrogen per ton of coal slurried in an anthracene oil solvent have been developed operating at about 1200 psi and 825.degree. F., primarily to produce clean fuel with little or no sulfur. These processes are described in "Fossil Fuel to Fuel Conversion," New Energy Technologies, pages 162-170, and Kloepper, D. L., Rogers, T. F., Wright, T. F., and Bull, W. C., "Solvent Processing of Coal to Produce a De-Ashed Product," R & D Report No. 9, prepared for Office of Coal Research, Department of Interior, Washington, D. C. by Spencer Chemical Division, Gulf Oil Corporation, Dec., 1965. The requirement of hydrogen and its recycle together with the relatively high temperatures and pressures of this process requires costly and extensive process equipment. More recently, catalytic dealkylation of coal with phenol and p-toluene sulfonic acid was reported by R. H. Moore, E. C. Martin, J. L. Cox and D. C. Elliott, in "Coal Liquefaction by Aromatic Interchange with Phenol and Catalytic Hydrogenolysis" in Industrial and Laboratory Alkylations, pages 417, 437, American Chemical Society, Symposium Series, 1977, editors L. F. Albright and A. R. Goldsby. This work again emphasizes the apparent necessity of proton donor catalysts to achieve acid catalyzed depolymerization of coal with phenol. Supercritical extraction of coal with toluene has been reported by Whitehead, J. C., and Williams, D. F., "Solvent Extraction of Coals by Supercritical Gases," J. Inst. of Fuel, Vol. 48, page 182, 1975, and as described in U.S. Pat. No. 3,558,468, teaches extraction of coal with benzene or toluene at temperatures above the critical temperature of the solvent and pressures in the range of 1000 to 5000 psi.